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December 1, 2006, 02:59 
Pressure drag, friction drag and total drag?

#1 
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Am I right about these three definitions?
1. Pressure drag can be obtained from the Function Calculator by integrating the total pressure with area at the flow direction, i.e. using Function: areaInt and Variable: Total Pressure. 2. Friction drag is obtained by integrating the wall shear with area at the flow direction, i.e. using Function: areaInt and Variable: Wall Shear. 3. Drag (pressure plus friction) is obtained from the force function specified in the flow direction. I've tried to obtain these values and they didn't match, i.e. Pressure drag (def. 1) + Friction drag (def. 2) not equaled to Drag (def. 3). Thanks in advance for your kind response. Cheng 

December 1, 2006, 09:20 
Re: Pressure drag, friction drag and total drag?

#2 
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1. Pressure drag can be obtained from the Function Calculator by integrating the total pressure with area at the flow direction, i.e. using Function: areaInt and Variable: Total Pressure.
I think think this has to be done as 3  2 = 1 2. Friction drag is obtained by integrating the wall shear with area at the flow direction, i.e. using Function: areaInt and Variable: Wall Shear. areaInt(component of wall shear in direction of interest) 

December 2, 2006, 01:24 
Re: Pressure drag, friction drag and total drag?

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Thanks Joe for your response. How about drag? Is it using the Function: Force for the flow direction?


December 2, 2006, 08:08 
Re: Pressure drag, friction drag and total drag?

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Yup.


December 2, 2006, 22:19 
Re: Pressure drag, friction drag and total drag?

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By these definitions, and in my case of air flow around a cube, the calculated Pressure Drag is 0.119644 N, Friction Drag is 0.000167 N. Summing these value give 0.119811 N. But the calculated Drag is actually 0.104207 N. Any idea why the value different?
Confused, Cheng 

May 3, 2017, 19:27 
Drag breakdown?

#6 
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Alp ASLAN
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Hi. I am working to Ahmed Body. I want to see drag breakdown values. Which mean; contributions to pressure drag from front part (Ck), slant rear end (Cs) and vertical rear end base (Cb). How can I see these values?
Thank you. 

May 4, 2017, 07:09 

#7 
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Glenn Horrocks
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1) Work out the formulas which those numbers are defined by
2) Enter formulas as CEL expressions 3) Get values from CEL expressions as monitor points in a simulation or in post processing in CFDPost 

May 4, 2017, 07:54 

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Alp ASLAN
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Quote:
Best regards. 

May 4, 2017, 17:48 

#9 
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Try the fluent forum


January 26, 2024, 13:46 

#10 
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nawres
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The total drag on the car can be expressed as the sum of two components: pressure drag and friction drag. Pressure drag is the drag caused by the difference in pressure between the front and rear of the car. It is proportional to the square of the car’s speed and the surface area of the car that is perpendicular to the airflow. Friction drag is the drag caused by the friction between the car’s surface and the air it moves through. It is proportional to the car’s surface area and the square of the car’s speed.
Therefore, the total drag on the car can be expressed as: D total=D pressure+D friction where D total is the total drag, D pressure is the pressure drag, and D friction is the friction drag. 

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